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(2) Dowel bars. Dowel bars are used to provide load transfer and prevent excessive vertical
displacements of adjacent slabs. There are some situations where the use of dowels is appropriate,
such as for creating load transfer where tying in to existing pavements.
(3) Stabilized base. A stabilized base can be used to improve load transfer effectiveness by
reducing joint deflections through increased support across a joint. Use a stabilized base for all
pavements less than 225 millimeters (9 inches) thick to provide improved load transfer and lower
deflections and stresses. A stabilized base may also be used for pavements greater than
225 millimeters (9 inches) thick to provide additional load transfer. Where thickened-edge joints are
used, the stabilized base is not required.
f. Joint Sealants. Joint sealants are used to provide a seal to reduce infiltration of water and
incompressibles. An effective joint seal will help retard and reduce distress related to free water and
incompressibles, such as pumping, spalling, faulting, and corrosion of mechanical load transfer devices.
Several pavement areas require fuel-resistant or blast-resistant joint sealants. Use jet fuel-resistant
sealants for all aprons. Use blast-resistant sealants for the first 305 meters (1,000 feet) of runways and
exits at runway ends. Use sealing compounds meeting ASTM D 1190, D 3405, or D 3406 for taxiways
and runway interiors.
(1) Types of sealant materials. The three major types of sealant materials are (a) field poured,
hot applied; (b) field poured, cold applied; and (c) preformed compression seals. These materials may
be jet fuel resistant (tar-based) or nonjet fuel resistant (typically asphalt based).
(a) Field poured, hot applied. This group of sealants includes rubberized asphalt sealant
and rubberized tar sealant. Rubberized asphalt joint sealants must meet ASTM D 1190, D 3405, or
D 3406. Rubberized tar sealants must meet ASTM D 3569 or D 3581.
(b) Field poured, cold applied. These are two-component, polymer-based, cold-applied
heat and jet fuel-resistant joint sealants. These sealants must meet Federal Specification SS-S-200E.
The Air Force and Navy recommends the use of silicone sealants that conform to NFGS 02522, 02562,
and ASTM 5893 in lieu of sealants that meed Federal Specification SS-S-200E.
(c) Preformed compression seals. The most common type of preformed compression seal
is the neoprene compression seal. Neoprene compression seals must satisfy ASTM D 2628. Preformed
compression seals may be used in the areas designated in NFGS-02522. Preformed compression seals
are designed to be in compression for their entire life. There is little bond between the compression seal
and the sidewalls of the joint to sustain tension.
(2) Joint reservoir design. The joint reservoir must be properly designed so that the joint sealant
can withstand compressive and tensile strains.
(a) Field poured sealants. The shape factor, which is defined as the ratio of the depth of the
sealant to the width of the joint, should be between 1.0 and 1.5. Dimensions of the joint sealant and
reservoir are shown in Figure 12-30. A backer rod or bond breaking tape must be used to help obtain a
proper shape factor and to prevent the joint sealant from bonding to the bottom of the joint reservoir.
Most field poured liquid joint sealants can withstand strains of approximately 25 percent of their original
width. Joint reservoir and sealant dimensions shown in Figure 12-30 are based on a slab size of 3.8 by
4.5 meters (12.5 by 15.0 feet).